This invention relates generally to hydraulic control systems and more specifically to a temperature responsive valve which can be used to modify the operation of a manual control valve.
In automotive automatic transmissions it is conventional to use a torque converter to couple engine power to the gear train through oil dependent upon the position of the transmission selector lever. Typically the transmission quadrant has six positoins including P (park), R (reverse), N (neutral), D (drive), I (intermediate) and L (low). The selector lever is mechanically coupled to a manual valve which is adapted to bring various hydraulic lines into and out of communication depending on the position selected. For example, when the transmission selector lever is moved to the drive position the manual valve moves to allow line pressure to be delivered to the forward clutch. The oil is metered to the forward clutch piston through an orifice to provide a smooth application of the clutch. However, as the transmission fluid warms up and becomes less viscous, the fluid flow becomes excessive and causes uneven shifting. This is particularly noticeable when shifting from reverse to drive. In U.S. Pat. No. 4,502,627, assigned to the assignee of the present invention, a temperature responsive flow control valve for use in a transmission is disclosed and claimed which compensates for temperature change to maintain fluid flow at a constant level and thereby provide smooth shifting. The flow control valve comprises a base having a first orifice of a selected minimum area and second parallel pasageway in the form of an elongated slot oriented to lie along an arc of movement of a thermostat metal element carrying a flag which slides on the base so that very small angular movement of the element causes the flag to cross over the entire width of the slot shaped orifice making adjustments in the effective orifice size as the temperature varies between two reference points. Although this valve mechanism is very effective its physical configuration is such that it can be used only in certain locations. That is, the arrangement of parts makes it unsuitable for use in small cylindrical passageways, for example.